Method and system for electromagnetic tracking with magnetic trackers for respiratory monitoring

ABSTRACT

A method and system using electromagnetic tracking to monitor the respiration of a patient. The system includes trackers attached to the patient that emit and receive a magnetic field that changes as the patient breathes. The changing field received by the tracker can be associated with the breathing states of the patient and used to generate a respiratory signal. The respiratory signal may be used to indicate when to advance an intervention tool during an intervention procedure on the patient. The same electromagnetic system may also be used to track the position of the intervention tool, further assisting the intervention procedure.

The present application relates generally to a method and system forrespiration-based guidance during interventional procedures.Interventional procedures can include interactive image-guided surgeryand interactive surgical procedures, such as biopsies. It findsparticular application with minimally invasive surgical proceduresperformed in conjunction with x-ray computed tomography (CT) imagingsystems. These procedures involve the use of surgical tools for biopsyor brachytherapy needles or the like for tissue sampling or planning orplacement of objects or instruments within the body of a subject, suchas a patient. It is to be appreciated, however, that the invention isalso applicable to a wide range of other imaging equipment andtechniques, for example ultrasonic and magnetic resonance imagingdevices, PET, SPECT, etc., and to a broad range of minimally invasivesurgical procedures including many forms of surgery for placing objectsor instruments at precise locations within a patient, such asinterventional radiology procedures and others. A typical goal ofinterventional procedures, along with most procedures involvingradiation, is to control the radiation delivery to minimize radiationexposure to the patient and the technician, such as a radiologist.

A CT scanner is commonly used for image guidance during interventionalprocedures. While it is possible to continuously watch the needleadvancement using CT fluoroscopy, this method is seldom used due to muchhigher radiation dose for the patient, hand exposure to the primary beamfor the radiologist, and inconvenience to manipulate the tool, such as,for example, a needle, inside a CT gantry bore. Therefore, a commonpractice is to use incremental tool advancement with periodicverification of the tool position by a single CT shot or scan.

One of the major challenges during such procedures is respiratorymotion. Due to such motion, the position of the internal organs in thetarget area during tool manipulation can differ significantly from theposition of the internal organs during the prior CT scan.

Respiratory monitoring has been used in the context of CT-guidedprocedures to select the optimal time for a CT scan, primarily to avoidmotion artifacts (e.g., by using respiratory gating) or forpost-procedure analysis of the recorded respiration wave (e.g., forradiation therapy planning).

One common practice used to address respiratory motion during aninterventional procedure is to have the patient hold his breath at thesame level during both the CT scan and afterwards, during theintervention tool insertion. However, various respiratory monitoringtechniques used with breath-holding and other breath-control protocolsmay not accurately determine the respiratory states of the subject. Inaddition, the components of respiratory monitoring systems typicallyserve only one purpose—to monitor respiration. Intervention toolguidance systems are also typically stand-alone systems that onlymonitor the location and position of the intervention tool during theintervention procedure.

The proposed system and method allow a user, such as, for example, atechnician, radiologist, or surgeon, to accurately monitor respirationusing an electromagnetic tracking system and thereby limit manipulationof the interventional tool to times when the positions of the internalorgans are close to their positions during a prior CT scan. The methodis based on continuous respiratory monitoring of the patient, bothduring the scan and during tool advancement throughout theinterventional procedure, with, in one embodiment, audio and/or visualnotification of when to start and/or stop the tool manipulation, forexample, needle advancement.

In one embodiment, an electromagnetic tracking system includes a firsttracker attached to a subject, wherein the first tracker includes anemitter to emit a magnetic field, a second tracker attached to thesubject, wherein the second tracker includes a first receiver to measurethe magnetic field, and logic to determine a position of the secondtracker relative to the first tracker based on the magnetic fieldmeasured by the first receiver and to generate a respiratory signalbased on the position of the second tracker relative to the firsttracker, wherein the position of the second tracker relative to thefirst tracker changes during a plurality of respiratory states of thesubject.

Numerous advantages and benefits will become apparent to those ofordinary skill in the art upon reading the following detaileddescription of several embodiments. The invention may take form invarious components and arrangements of components, and in variousprocess operations and arrangements of process operations. The drawingsare only for the purpose of illustrating many embodiments and are not tobe construed as limiting the invention.

The descriptions of the invention do not limit the words used in theclaims in any way or the scope of the claims or invention. The wordsused in the claims have all of their full ordinary meanings.

In the accompanying drawings, which are incorporated in and constitute apart of the specification, embodiments of the invention are illustrated,which, together with a general description of the invention given above,and the detailed description given below, serve to exemplify embodimentsof this invention.

FIG. 1 illustrates an exemplary CT imaging system with an exemplaryelectromagnetic tracking system;

FIG. 2 illustrates an exemplary integrated apparatus with exemplaryrespiratory monitoring, imaging, and interventional procedure systems;

FIG. 3 is a drawing of an exemplary electromagnetic tracking assembly;

FIG. 4 is a drawing of another exemplary electromagnetic trackingassembly showing an exemplary three-coil configuration;

FIG. 5 is a drawing of an exemplary universal device;

FIG. 6 is a cross-sectional drawing of an exemplary multimodal fiducialmarker;

FIG. 7 is a drawing of components of an exemplary respiratory monitorutilizing an electromagnetic tracking system;

FIG. 8 is a drawing of components of another exemplary respiratorymonitor on a patient using an electromagnetic tracking system;

FIG. 9 is a cross-sectional drawing of a patient undergoing aninterventional procedure with exemplary electromagnetic trackingdevices;

FIG. 10 includes cross-sectional drawings of a patient undergoing aninterventional procedure;

FIG. 11 is a schematic/block diagram representation of an exemplarysystem for respiratory monitoring and indicating intervention tooladvancement timing during an intervention procedure;

FIG. 12 shows an exemplary waveform representing a patient's respirationstate during normal breathing;

FIG. 13 shows an exemplary bar graph having a height representative ofan inhalation/exhalation level of a patient;

FIG. 14 is a cross-sectional drawing of a patient undergoing aninterventional procedure with exemplary electromagnetic tracking devicesto monitor the patient's respiration and the location and orientation ofan intervention tool;

FIG. 15 is a block diagram representing an exemplary system 1500 forrespiratory monitoring, intervention tool navigation, and indicatingintervention tool advancement timing;

FIG. 16 is a flowchart of an exemplary method of generating arespiratory signal using an electromagnetic respiration monitor;

FIG. 17 is a flowchart of another exemplary method of generating arespiratory signal using an electromagnetic respiration monitor;

FIG. 18 is a flowchart of an exemplary method of generating arespiratory signal and a virtual representation of an intervention toolusing an electromagnetic tracking system; and

FIG. 19 is a flowchart of an exemplary method of indicating when toadvance an intervention tool during an intervention procedure.

In one embodiment, an exemplary CT imaging system 100 and an exemplaryelectromagnetic tracking system 150 are shown in FIG. 1. A CT imagingacquisition system 102 includes a gantry 104 and a table or othersupport 106 which may move along the z-axis. A patient or other subjectto be imaged (not shown in FIG. 1) lies down on the table 106 and ismoved to be disposed within an aperture or bore 108 in the gantry 104.Once the patient is in position, an x-ray source 110 and an x-raydetector 112 rotate together around the bore 108 to record CT imagingdata. Other imaging system modalities may also be used in conjunctionwith the claimed invention, including, for example, cone beam CT, otherx-ray based imaging, ultrasound imaging, magnetic resonance imaging(MRI), positron emission tomography (PET) imaging, and the like.

The CT imaging acquisition system 102 can then pass the CT imaging dataon to a CT imaging processing and display system 114 through acommunication link 101. Although the systems 102 and 114 are shown anddescribed here as being separate systems for purposes of illustration,they may in other embodiments be part of a single system. The CT imagingdata passes to an image processor 116 which can store the data in amemory 118. The image processor 116 electronically processes the data toperform an image reconstruction. The image processor 116 can show theresulting images on an associated display 120. A user input 122 such asa keyboard and/or mouse device may be provided for a user to control theprocessor 116.

An exemplary electromagnetic tracking system 150 is also shown inFIG. 1. The tracking system 150 includes tracking and/or markingcomponents 160, such as trackers and/or markers that can monitormovement associated with a subject's respiration and register componentswith the subject's image data, as described in more detail below. Thetracking and/or marking components 160 can provide one or more signals162 to an electromagnetic tracking system processor 164, which can storedata and other information in a memory 166. The electromagnetic trackingsystem processor 164 may include logic for determining relative movementand/or position between the tracking and/or marking components 160. Theelectromagnetic tracking system processor 164 may also produce anintervention tool advancement indicator signal 168, which can indicatewhen the patient's respiration state signifies that the patient'sposition is suitable for advancing an intervention tool (not shown). Inanother embodiment, the electromagnetic tracking system processor 164can provide a signal to an intervention advancement processor, which canproduce the intervention tool advancement indicator signal 168. Inanother embodiment, these processors may be combined. The advancementindicator signal 168 may be used to drive one or more indicatingdevices, such as, for example, an audible indicator, such as speaker170, and/or a visual indicator, such as display 172.

Many of the aforementioned functions can be performed as software logic.“Logic,” as used herein, includes but is not limited to hardware,firmware, software and/or combinations of each to perform a function(s)or an action(s), and/or to cause a function or action from anothercomponent. For example, based on a desired application or needs, logicmay include a software controlled microprocessor, discrete logic such asan application specific integrated circuit (ASIC), or other programmedlogic device. Logic may also be fully embodied as software.

“Software,” as used herein, includes but is not limited to one or morecomputer readable and/or executable instructions that cause a computer,processor, or other electronic device to perform functions, actions,and/or behave in a desired manner. The instructions may be embodied invarious forms such as routines, algorithms, modules or programsincluding separate applications or code from dynamically linkedlibraries. Software may also be implemented in various forms such as astand-alone program, a function call, a servlet, an applet, instructionsstored in a memory such as memories 118 and 166, part of an operatingsystem or other type of executable instructions. It will be appreciatedby one of ordinary skill in the art that the form of software isdependent on, for example, requirements of a desired application, theenvironment it runs on, and/or the desires of a designer/programmer orthe like.

The systems and methods described herein can be implemented on a varietyof platforms including, for example, networked control systems andstand-alone control systems. Additionally, the logic shown and describedherein preferably resides in or on a computer readable medium such asthe memory 118 and/or 166. Examples of different computer readable mediainclude Flash Memory, Read-Only Memory (ROM), Random-Access Memory(RAM), programmable read-only memory (PROM), electrically programmableread-only memory (EPROM), electrically erasable programmable read-onlymemory (EEPROM), magnetic disk or tape, optically readable mediumsincluding CD-ROM and DVD-ROM, and others. Still further, the processesand logic described herein can be merged into one large process flow ordivided into many sub-process flows. The order in which the processflows herein have been described is not critical and can be rearrangedwhile still accomplishing the same results. Indeed, the process flowsdescribed herein may be rearranged, consolidated, and/or re-organized intheir implementation as warranted or desired.

The exemplary electromagnetic tracking system 150 may be a stand-alonesystem or in other embodiments may be fully or partially integrated withthe exemplary CT imaging system 100 to form a combined system.

Referring now to FIG. 2, another embodiment is shown with an exemplaryintegrated apparatus 200, which includes an exemplary imaging system 201and an exemplary electromagnetic tracking system 202. The integratedapparatus 200 is particularly well suited for planning and executingminimally invasive interventional procedures, such as, for example,biopsies, in-vivo placement of instruments and/or objects within apatient, etc., as described above.

The electromagnetic tracking system 202 includes tracking and/or markingcomponents 204, which can facilitate respiratory monitoring, imageregistration, and intervention tool navigation, as discussed in moredetail below. In one embodiment, the tracking and/or marking components204 may include a belt 206 adapted for attachment around the abdomen orchest of a patient and two or more electromagnetic tracking devices 207.In this embodiment, the relative movement of the electromagnetictracking devices 207 can be used for generating a signal correspondingto the displacement of a patient's abdomen during respiration. Thetracking and/or marking components 204 are connected to the imagingsystem 201 at a suitable electronic connection point 208.

With continued reference to FIG. 2, the imaging system 201 includes avolumetric diagnostic CT imaging apparatus/scanner 210 as shown. The CTimaging apparatus 210 is disposed in axial alignment with a patienttable 212 and support 214 such that a patient or subject on the support214 surface can be moved into and through a bore 216 of the CT scanner210. The CT scanner 210 includes an x-ray tube mounted for rotationabout a pre-selected plane. The x-ray tube can project a fan shaped beamof radiation through a ring 218 of radiation translucent material,through the patient support 214, through a region of interest or targetarea of the patient, and to a ring or arc of radiation detectorsdisposed opposite the x-ray tube. As the x-ray tube rotates within theplane, a series of data lines are generated, which data lines arereconstructed into at least a slice image using well known techniques bya reconstruction processor included in a control console 220 operativelyconnected with the CT scanner 210.

As is well known in the art, in some embodiments, the patient support214 can move longitudinally along the z-axis as the x-ray tube isrotating around the subject such that a selected volume of the patientis scanned along a spiral path or a series of slices. The position ofthe x-ray tube is monitored by a rotational position encoder and thelongitudinal position of the patient support is monitored by similarposition encoders disposed within the table 212. In other embodiments,volumetric data may be obtained without longitudinal movement. Thereconstruction processor can reconstruct a volumetric imagerepresentation from the generated data lines. The control console 220includes one or more human readable display devices, which can be in theform of an operator monitor or display 222 and at least one operatorinput device 224, such as, for example, a keyboard, track ball, mouse,or the like.

With continued reference to FIG. 2, an exemplary intervention tool 230is shown above the patient support 214. An exemplary intervention tooladvancement indicator device 232 is shown opposite the intervention tool230. The intervention tool advancement indicator device 232 may include,for example, an audible indicator, such as speaker 170, and/or a visualindicator, such as display 172, as shown in FIG. 1. The interventiontool 230 and intervention tool advancement indicator device 232 areshown supported from overhead on a track or by other means 234 atop theCT scanner 210. In this embodiment, the intervention tool 230 andintervention tool advancement indicator device 232 are shown inexemplary positions that may be convenient for a user performing anexemplary interventional procedure on the subject. However, thepositioning of any of the devices shown in this embodiment may bearranged or supported differently in other embodiments. The interventiontool advancement indicator device 232 can be oriented or moved intoselected positions on the support system 234 for easy viewing and/orhearing by a user.

As shown in FIG. 2, the exemplary control console 220 may include bothan image processor, an electromagnetic tracking system processor, and anintervention advancement processor (not shown), such as, for example,the image processor 116 and the electromagnetic tracking systemprocessor 164 of FIG. 1. In various embodiments, these processors may bephysically and/or electronically integrated within the control console220 and/or each other. In another embodiment, the electromagnetictracking system processor 164 may be included in a device with theintervention tool advancement indicator device 232 and/or theintervention advancement processor.

FIG. 3 is a drawing of an exemplary electromagnetic tracking assembly300. The assembly 300 includes an exemplary electromagnetic trackingdevice or tracker 310 and an exemplary base 320 for attachment to thesubject or patient, via, for example, an adhesive layer. Theelectromagnetic tracking device 310 may be one of the tracking and/ormarking components 204 as mentioned above in relation to FIG. 2, and inparticular, one of the electromagnetic tracking devices 207. Theelectromagnetic tracking device 310 can be used as part of spatialtracking or localizing system based on known electromagnetic technology.In particular, the electromagnetic tracking device 310 includes anemitter that emits a magnetic field generated by one or more coils or areceiver that measures the magnetic field around itself when positionedin the emitted magnetic field using one or more coils. Anelectromagnetic tracking system, such as, for example, system 202 shownin FIG. 2, requires at least one electromagnetic tracking device 310with an emitter and at least one electromagnetic tracking device 310with a receiver.

A processor, such as, for example, the electromagnetic tracking systemprocessor 164 of FIG. 1, can utilize signals from the electromagnetictracking devices 310, which are indicative of the magnetic field emittedby an emitter and measured by a receiver, to determine the relativeposition and/or orientation of the electromagnetic tracking devices 310.For example, electromagnetic tracking devices 310 with single coilemitter and receiver designs may allow for the determination of therelative distance between the electromagnetic tracking devices 310,whereas electromagnetic tracking devices 310 with multiple coils mayallow for the determination of the relative distance and orientation ofthe electromagnetic tracking devices 310. Electromagnetic localizingsystems are ergonomic and easy to use because direct line-of-sightvisualization is not required, allowing obstacles to be positionedbetween the emitter and the receiver, including, for example, a hand, asurgical drape, an intervention tool, etc., without impacting theaccuracy of the spatial measurements. Although the electromagnetictracking devices 207, 310 shown in FIGS. 2 and 3 are drawn as relativelylarge cubes, the electromagnetic tracking devices 207, 310 and anyothers mentioned herein may be any size and/or shape suitable for anyparticular application of an electromagnetic tracking system.

FIG. 4 is a drawing of an exemplary electromagnetic tracking device 400including an outer covering 410 and three coils 420 imbedded inside thedevice 400. In this embodiment, the three coils 420 are all orientedorthogonally to each other, forming a three-axis spatial reference gridor coordinate system. Two-coil designs may also be suitable for certainapplications. Although the three coils 420 are shown with their endsmeeting at a common vertex, this need not be the case. In otherembodiments, coils may be separated and oriented in non-orthogonalconfigurations.

FIG. 5 is a drawing of an exemplary universal device 500 that includesan exemplary electromagnetic tracking device 510, an exemplary base 520for attachment to the subject or patient, and an exemplary fiducialmarker 530. The electromagnetic tracking device 510 may be one of theelectromagnetic tracking devices 310, 410 mentioned above. Althoughshown together in universal device 500, in other embodiments theelectromagnetic tracking device 510 and fiducial marker 530 may be usedas separate components, for example, as part of the tracking and/ormarking components 160 shown in FIG. 1. In other embodiments, theelectromagnetic tracking device 510 and fiducial marker 530 may beintegrated into one housing or covering.

The fiducial marker 530 allows for image registration. In particular,the fiducial marker 530 is made of a material that can be detectedduring the scan of the patient by, for example, the CT scanner 210 shownin FIG. 2. However, in addition to CT, imaging modalities may includefluoroscopy, positron emission tomography (“PET”), micro PET, singlephoton emission computed tomography (“SPECT”), micro SPECT, magneticresonance (“MR”), ultrasound, and others. Although shown in FIG. 5 as acube, in other embodiments, the fiducial marker 530 and any othersmentioned herein may be any size, shape, and material suitable fordetection and registration of the image data from the scan associatedwith the interventional procedure, including multimodal fiducial markersfor registration of different types of imaging data.

By including the fiducial marker 530 in the view of a scan of a patient,the physical location of the fiducial marker 530 relative to the area ofinterest in the patient, such as, for example, the target area of aninterventional procedure, is known. The physical location of thefiducial marker 530 relative to the electromagnetic tracking device 510is also known. By combining this information, the acquired images can bealigned in a common spatial reference grid or coordinate system fornavigation of an intervention tool (also outfitted with a trackingdevice) to the target area, as discussed in more detail below.

FIG. 6 is a cross-sectional drawing of an exemplary multimodal fiducialmarker 600 that may be used as the fiducial marker 530. Morespecifically, a first portion 610 of the multimodal fiducial marker 600may be a radiopaque material. A radiopaque material is a material whichis opaque to x-ray radiation, so it is visible in x-ray photographs andunder fluoroscopy. Materials which are dense enough to be opaque tox-ray radiation are also typically visible in an ultrasound scan. Thusthe first portion 610 will be visible to CT, fluoroscopy, and otherx-ray based imaging systems, as well as ultrasound imaging systems. Thefirst portion 610 of the exemplary fiducial marker 600 may beadvantageously shaped in the form of a sphere. Such a spherical geometryallows the first portion 610 to be consistently identified from allangles and allows for accurate localization of the center of thefiducial marker 600. The spherical shape of the first portion 610 alsoallows the fiducial marker 600 to be easily detectable such that theimage registration process may be automated. However, other shapes andgeometries known in the art may be used. The second portion 620 of themultimodal fiducial marker 600 may be radioactive. For example, thesecond portion 620 may be comprised of a porous material which absorbs aradioactive material. Once the porous material is at least partiallysaturated with the radioactive material, the second portion 620 isactivated. The resulting radioactivity of the second portion 620 will bevisible to PET, micro PET, SPECT, and micro SPECT imaging systems. Thefiducial marker 600 also includes an attachment means for attaching thefiducial marker 600 to a base or the imaged subject, or an apparatus onor in which the imaged subject is disposed.

FIG. 7 is a drawing of components of an exemplary respiratory monitor700 utilizing an electromagnetic tracking system, similar to thetracking and/or marking components 204, shown in FIG. 2. In thisembodiment, the respiratory monitor 700 includes a belt 710 adapted forattachment around the abdomen or chest of a patient and twoelectromagnetic tracking devices 720, 730. FIG. 8 is a drawing ofcomponents of another exemplary respiratory monitor 800 on a patient 810using an electromagnetic tracking system. In this embodiment, therespiratory monitor 800 includes three electromagnetic tracking devices820, 830, 840 attached directly to the patient 810. In otherembodiments, any of the electromagnetic tracking devices 720, 730, 820,830, 840 shown in FIGS. 7 and 8 can be replaced with or enhanced withone or more additional electromagnetic tracking devices, fiducialmarkers, and/or universal devices for use in other applications.

FIG. 9 is a cross-sectional drawing of a patient 910 undergoing aninterventional procedure with exemplary electromagnetic tracking devices940, 950, 960 used to monitor the patient's respiration. The patient 910is shown on a support 920 in front of a bore of an exemplary CT scanner930. An exemplary intervention tool 970 is also shown advancing towardsa target area 980 within the patient 910. As described above, theelectromagnetic tracking devices 940, 950, 960 are part of anelectromagnetic tracking system used to monitor the respiration of thepatient 910 during scans and the intervention procedure.

Generally, the electromagnetic tracking system tracks the respiration ofthe patient using the electromagnetic tracking devices 940, 950, 960 andcan generate a signal or other representation of the patient'srespiration state. The signal may be used to indicate to the user whento advance the intervention tool 970. In particular, the intent is toadvance the intervention tool 970 when the patient's respiration stateis at the same state as when the patient 910 was scanned to produce animage data set. As discussed above, the patient's internal organs andchest cavity may move during respiration, but this movement can becorrelated to the patient's respiration states. It is beneficial andpreferable to advance the intervention tool 970 when the user knowswhere the patient's internal organs and chest cavity are positioned.Therefore, knowing the respiration state of the patient 910 during thescan, which is the source of the image data that the user uses to guidethe intervention tool 970 during intervention tool advancement, allowsthe system to indicate to the user when the patient's internal organsand chest cavity will be in the same position again, i.e., when thepatient 910 is in the same respiration state. In one embodiment, and asdiscussed in more detail below, the patient 910 may be asked to hold hisbreath when the system indicates that the patient's respiration state isthe same state as when the scan was taken, thereby allowing the user toadvance the intervention tool 970 while the patient is in the sameposition as when the scan was taken. In another embodiment, and alsodiscussed in more detail below, the patient 910 may breathe normally,such that when the system indicates that the patient's respiration stateis the same or is about to be in the same as when the scan was taken,the user can advance the intervention tool 970 a relatively small amountwhile the patient 910 is in the same position as when the scan wastaken.

An electromagnetic tracking system processor can include logic tocorrelate the relative positions of the electromagnetic tracking devices940, 950, 960 to a patient's respiration state and generate arespiratory signal or respiration representation. FIG. 10 includescross-sectional drawings of the patient 910 undergoing theinterventional procedure. The patient's respiration is monitored withelectromagnetic tracking devices 940, 950, 960, shown in an inhale state(FIG. 10A, where the cross-section of the patient's chest cavity is morerounded) and in an exhale state (FIG. 10B, where the cross-section ofthe patient's chest cavity is flatter). In this simplified example, theorientations and relative distances between electromagnetic trackingdevices 940 and 950 are shown in two dimensions during the exemplaryinhale and exhale states. As shown in FIG. 10A, D1 and D2 are therelative distances between devices 940 and 950 in two dimensions duringan inhale state. Also during the inhale state, D3 is the distancebetween the tip of the intervention tool 970 and the target area 980. Asshown in FIG. 10B, D1′ and D2′ are the relative distances betweendevices 940 and 950 during an exhale state. Also during the exhalestate, D3′ is the distance between the tip of the intervention tool 970and the target area 980. As shown in these drawings, the relativeposition of devices 940 and 950 changes during the exemplary inhale andstates of the patient 910. In particular, D1 is less than D1′ and D2 isgreater than D2′. These changes in relative position can be tracked anddirectly correlated to the respiration states of the patient 910. Thesignificance of these changes is depicted by the change in the distancebetween the tip of the intervention tool 970 and the target area 980during the inhale and exhale states. In particular, D3 is significantlygreater than D3′, meaning that as the patient 910 exhales, the tip ofthe intervention tool 970 is drawn closer to the target area 980,without any advancement of the intervention tool 970 by the user. Inother embodiments, the relative positions of devices 940 and 950 may betracked in three dimensions and device 960 and possibly other devicesmay also be used to monitor respiration. In other embodiments, spatialorientations may also be tracked in addition to or instead of relativepositions, including the use of angular measures and relationships.References to “position” in this application can include both positionand orientation. Different intervention procedures may require higher orlower degrees of accuracy, may involve more or less patient movementduring respiration, etc., requiring different configurations of theelectromagnetic tracking system and/or tracking algorithms.

FIG. 11 is a schematic/block diagram representation of an exemplarysystem 1100 for respiratory monitoring and indicating intervention tooladvancement timing during an intervention procedure. System 1100includes an exemplary scanning system 1110, such as, for example, a CTscanner. The system 1100 further includes exemplary tracking components1112, such as, for example, electromagnetic tracking devices, a belt,etc., as mentioned above. In other embodiments, markers, such as, forexample, fiducial markers, may be incorporated for image registration.

As illustrated, an electromagnetic tracking system processor 1116receives one or more signals from the tracking components 1112 and isoperatively connected with several components of the system 1100,including a memory 1118, a user interface 1120, one or more interventiontool advancement indicators 1122, and a scanning systemcontroller/gating device 1124. The memory 1118 may be used to storevarious software, logic, and/or parameters utilized by theelectromagnetic tracking system processor 1116, including, for example,measured values and parameters associated with the components 1112 andthe respiration states of the subject, associated intervention tooltriggering/threshold values and/or levels, algorithms for determiningtriggering/threshold points and/or levels, user selected values, imagedata, etc., as discussed in more detail below. The user interface 1120can include user input and display devices and may be integrated as partof control console 220 of FIG. 2.

The exemplary intervention tool advancement indicators 1122 may includeone or more audible indicators, such as speaker 1126, and/or one or morevisual indicators, such as displays 1128, 1130. The speaker 1126 canproduce a continuous sound, instances of the same sound, or instances ofdifferent sounds to indicate when to start and stop intervention tooladvancement. For example, a continuous beep or “on” and “off” beeps maybe used for indicating when to advance the intervention tool.

The displays 1128, 1130 can include visual indicia of the patient'sbreathing and/or indicate when to advance the intervention tool. In oneembodiment, a display 1128, 1130 may simply display a visual cue, suchas, for example, a word or color (e.g., red and/or yellow followed bygreen) to indicate when to advance the intervention tool. In otherembodiments, as shown in FIG. 11, the displays 1128, 1130 can depict arepresentation of the patient's breathing. Exemplary display 1128 showsa waveform 1132 having an amplitude representing the respiration of apatient. Exemplary display 1130 shows a bar graph 1134 having a heightrepresentative of an inhalation/exhalation level of the patient on ascale of percentage of vital capacity (% VC). It is to be appreciatedthat although a waveform and bar graph are illustrated, other forms ofpatient breathing images can be used as well such as, for example, agraduated cylinder, a progress bar, an animated diaphragm, and the like.

In addition to driving intervention tool advancement indicators 1122,the electromagnetic tracking system processor 1116 can be used toprovide a signal to control the scanning system 1110. For example,control/gating device 1124 may be used to control or provide a signal tothe scanning system 1110 to scan the patient at a particular respirationstate, for example, at the same respiration state during which the userwas advancing the intervention tool. This may be helpful duringconfirmation scans. In one embodiment, the control/gating device 1124may be integrated as part of control console 220 of FIG. 2.

An exemplary intervention procedure includes scanning stages andintervention tool advancement stages. During the scanning stage, ascanner scans a patient. An electromagnetic tracking system may be usedto monitor the patient's breathing state during the scan, producing oneor more signals indicative of the patient's breathing states. Thepatient may be asked to breathe normally or may be asked to hold hisbreath during scanning. The scanner produces an image data set, such as,for example, a volumetric data set, suitable to assist and guide theuser during the subsequent intervention procedure. Exemplary imageprocessing devices may be as described above in FIGS. 1 and 2. Anintervention tool may be scanned with the target area of the patient,although this need not be the case in all embodiments. In someembodiments, it may be helpful to have the intervention tool scannedwith the patient to establish a reference starting position of theintervention tool on the scan and in the image data set. During thescanning stage, one or more scans may be taken of the patient. For eachscan, an electromagnetic tracking system processor reads the respirationsignal(s) from the tracking components (e.g., electromagnetic trackingdevices) and associates the signal readings with the respective imagedata set. The respiration signal(s) is also associated with a particularrespiration state of the patient. All of this data may be saved inmemory.

An intervention tool advancement stage follows the scanning stage.During the tool advancement stage, the patient is removed from thescanner, allowing for intervention tool advancement without additionalexposure to radiation from the scanner. The electromagnetic trackingsystem continues to monitor the patient's breathing states and producesa respiration signal indicative of the patient's breathing states. Thepatient may be asked to breathe normally or may be asked to hold hisbreath during intervention tool advancement. The electromagnetictracking system can drive an intervention tool advancement indicatorthat indicates when the patient's respiration state is at the same stateas it was during the scan that created the image data set being used bythe user to guide advancement of the intervention tool.

In this manner, the user is alerted to when the patient's internalorgans and chest cavity are in the proper position to advance theintervention tool, by tracking the patient's respiration. In particular,the electromagnetic tracking system processor can monitor the patient'srespiration state for certain thresholds/triggering points to drive theintervention tool advancement indicator, which indicates to the user asuitable time to advance the intervention tool. In particular, when theelectromagnetic tracking system indicates that the patient's respirationstate is the same as during the scan, via the intervention tooladvancement indicator, an indication is provided to the user that it isa suitable time to advance the intervention tool, because the user knowsthat the patient's target area should be in a position matching theimage data set.

FIGS. 12 and 13 show exemplary graphical representations of a patient'srespiration states used for triggering an intervention tool advancementindicator. The representations shown in FIGS. 12 and 13 may berepresentative of the tracking and triggering algorithms utilized by anelectromagnetic tracking system processor and/or an interventionadvancement processor, which in some embodiments may also be displayedon a display associated with an intervention tool advancement indicator(e.g., display 172 in FIG. 1, displays 222, 232 in FIG. 2, and displays1132, 1134 in FIG. 11).

FIG. 12 shows an exemplary waveform 1202 representing a patient'srespiration state during normal breathing, but with variations in timeand lung capacity fill levels from one breath to another. In thisembodiment, waveform 1202 can be generated by the exemplaryelectromagnetic tracking system processor mentioned above. Waveform 1202rises and falls over time while the patient inhales and exhales,respectively. The peaks and valleys shown in FIG. 12 may correspond tothe inhale and exhale states shown in FIG. 10, respectively. Target line1204 represents the respiration state corresponding to an associatedimage data set for use during the intervention procedure and from anearlier scan. Each time the patient's real-time respiration state 1202is at (i.e., crosses) line 1204, the patient's respiration state (andthe position of the patient's internal organs and chest cavity)corresponds to the respiration state (and position) associated with theimage data set. In this embodiment, the processor uses these crossingpoints as triggering points 1210 to drive an intervention tooladvancement indicator, which indicates to the user a suitable time toadvance an intervention tool.

FIG. 13 shows an exemplary bar graph 1302 having a height representativeof an inhalation/exhalation level of the patient on a scale ofpercentage of vital capacity (% VC). In this embodiment, bar graph 1302rises and falls over time while the patient inhales and exhales,respectively. Target line 1304 represents the respiration statecorresponding to an associated image data set for use during theintervention procedure and from an earlier scan. Each time the patient'sreal-time respiration state 1302 is at line 1304, the patient'srespiration state (and the position of the patient's internal organs andchest cavity) corresponds to the respiration state (and position)associated with the image data set. In this embodiment, the patient maybe asked to hold his breath when the graph is at line 1304, during whichtime the user can advance the intervention tool.

Various parameters and algorithms associated with the intervention tooladvancement indicator, such as, start time, stop time, length of time todrive the indicator, responses to intervention, patient, and/or outsidefactors, etc., may be determined as part of a planning phase to developan intervention procedure plan, which typically precedes theintervention procedure. In some embodiments, the intervention procedureplan may be modified during the intervention procedure, based on variousfactors, including, for example, a confirmation scan.

In addition to or instead of driving an intervention tool advancementindicator, the electromagnetic tracking system may be used to track theposition and/or orientation of an intervention tool. FIG. 14 is across-sectional drawing of patient 910 undergoing an interventionalprocedure with exemplary electromagnetic tracking devices 940, 950, 960used to monitor the patient's respiration, exemplary electromagnetictracking devices 960, 1410 used to monitor the location and orientationof intervention tool 1430, and fiducial marker 1420 to register theelectromagnetic tracking system with image data. In this embodiment,electromagnetic tracking device 960 includes an emitter that is used fortracking electromagnetic tracking devices 940, 950, 1410, which eachinclude a receiver. In this manner, the same electromagnetic trackingsystem may be used to monitor the patient's respiration states, drive anintervention tool indicator, and/or track the position and orientationof an intervention tool 1430. In one embodiment, electromagnetictracking device 960 and fiducial marker 1420 may be integrated into oneuniversal device.

By including the fiducial marker 1420 in the view of a scan of thepatient 910, the location of the fiducial marker 1420 relative to thetarget area 980 is known. The location of the fiducial marker 1420relative to the electromagnetic tracking device 960 is also known. Bycombining this information, the acquired images can be aligned with thetracking components in a common spatial reference grid or coordinatesystem (i.e., localized space) for navigation of the intervention tool1430, outfitted with electromagnetic tracking device 1410, to the targetarea 980. In sum, the fiducial marker 1420 is detected in the image datafrom the scanning system and used to register images of the patient 910with components involved with the real-time interventional procedure.Associating the electromagnetic tracking device 960 with the fiducialmarker 1420 enables defining a common referential system being utilizedby both the imaging and localizing systems, so that data of the imagingand localizing systems can be registered together.

The spatial position and orientation of the intervention tool 1430 maybe determined using electromagnetic tracking device 1410 in the samemanner as described above in relation to the electromagnetic trackingdevices 940, 950, 960 used for respiratory monitoring. In otherembodiments, more than one electromagnetic tracking device may beassociated with the intervention tool 1430. In some embodiments, theelectromagnetic tracking device 1410 will be required to be asophisticated three-coil receiver to accurately determine the spatialposition and orientation of the whole intervention tool 1430 (instead ofjust the position of the electromagnetic tracking device 1410) in thelocalization system, for example, in applications where the path of theintervention tool 1430 advancement is important. Although theelectromagnetic tracking device 1410 is shown at the end of theintervention tool 1430 away from the advancing tip in FIG. 14, theelectromagnetic tracking device 1410 may be located at any location onthe intervention tool 1430, including at the advancing tip. Inembodiments where the electromagnetic tracking device 1410 is notlocated at the advancing tip of the intervention tool 1430, it is knownin the art how to track the tip by knowing the relationship between theelectromagnetic tracking device 1410 and the tip. To maintain suitableaccuracy, in some embodiments, the offset distance between theelectromagnetic tracking device 1410 and the tip of the interventiontool 1430 will be minimized.

In this manner, the position of the intervention tool 1430 can becorrelated to the image data of the patient 910, allowing the system tovirtually display the intervention tool 1430 in the images of thepatient 910. The registration and tracking systems enable constructingand displaying a navigation image, wherein a virtual representation ofthe spatial position of the intervention tool 1430 is displayed on imagedata from the imaging system using the localization system defined bythe electromagnetic tracking devices, including device 1410.

FIG. 15 is a block diagram representing an exemplary system 1500 forrespiratory monitoring, intervention tool navigation, and indicatingintervention tool advancement timing. System 1500 includes an exemplaryimaging system 1510, such as, for example, a CT scanner. The system 1500further includes exemplary tracking and/or marking components 1512, suchas, for example, electromagnetic tracking devices and fiducial markers,to support respiration 1530 and intervention tool position 1532 trackingand registration functions.

As illustrated, an electromagnetic tracking system processor 1516receives signals from the tracking components 1512 (e.g.,electromagnetic tracking devices), indicative of respiration 1530 andtool position 1532, and image data from imaging system 1510. Theprocessor 1516 may be operatively connected with several othercomponents of the system 1500, including a memory 1518, a user interface1520, one or more intervention tool advancement indicators 1540, and anavigation display 1550. The memory 1518 may be used to store varioussoftware, logic, values, and/or parameters utilized by theelectromagnetic tracking system processor 1516, including, for example,measured values and parameters associated with the components 1512, therespiration states of the subject, the positions and orientations of thecomponents 1512 and an intervention tool, associated intervention tooltriggering/threshold values and/or levels, algorithms for determiningtriggering/threshold points and/or levels, user selected values, imagedata, registration data, tool dimensions, etc. The user interface 1520can include user input and display devices and may be integrated as partof control console 220 of FIG. 2.

The electromagnetic tracking system processor 1516 can use the data andsignals described above for the following functions: respirationmonitoring 1534; localization and position/orientation detection 1536;and registration 1538. The electromagnetic tracking system processor1516 can execute logic to perform the various calculations anddeterminations associated with each of these functions, as describedabove. These functions can be used by the electromagnetic trackingsystem processor 1516 to drive an intervention tool advancementindicator 1540 and intervention tool navigation display 1550. Thenavigation display 1550 can display the image data of a patient alongwith a virtual representation of the intervention tool in real time,including during the intervention procedure. The navigation display 1550can be used by the user to guide the advancement of the interventiontool. The navigation display 1550 may be a separate display or may beincorporated with any of the displays mentioned above (e.g., display 172in FIG. 1, displays 222, 232 in FIG. 2, and displays 1132, 1134 in FIG.11). In one embodiment, the advancement indicator 1540 is incorporatedwith the navigation display 1550.

FIGS. 16-19 describe exemplary methods associated with utilization ofelectromagnetic tracking systems, including, for example, thosementioned above. Further embodiments of similar methods may includeother additional steps, or omit one or more of the steps in theillustrated methods. Also, the order in which the process flows hereinhave been described may be rearranged while still accomplishing the sameresults. Thus the process flows described herein may be added to,rearranged, consolidated, and/or re-organized in their implementation aswarranted or desired.

FIG. 16 is a flowchart of an exemplary method of generating arespiratory signal using an electromagnetic respiration monitor, such asthose mentioned above. At step 1610, a first tracker attached to asubject emits a magnetic field. Next, at step 1620, a second trackerattached to the subject measures the magnetic field emitted by the firsttracker. At step 1630, the relative position of the first and secondtrackers is determined based on the magnetic field measured by thesecond tracker. The changing field received by the tracker can beassociated with the breathing states of the subject and used to generatea respiratory signal. At step 1640, the respiratory signal is generatedbased on the position of the second tracker relative to the firsttracker.

FIG. 17 is a flowchart of another exemplary method of generating arespiratory signal using an electromagnetic respiration monitor, such asthose mentioned above. Steps 1710-1720 are similar to steps 1610-1620mentioned above. At step 1730, a third tracker attached to the subjectmeasures the magnetic field emitted by the first tracker. At step 1740,the relative position of the first, second, and third trackers isdetermined based on the magnetic field measured by the second and thirdtrackers. The changing field received by the trackers can be associatedwith the breathing states of the subject and used to generate arespiratory signal. At step 1750, the respiratory signal is generatedbased on the relative position of the first, second, and third trackers.

FIG. 18 is a flowchart of an exemplary method of generating arespiratory signal and a virtual representation of an intervention toolusing an electromagnetic tracking system, such as those mentioned above.Steps 1810-1820 are similar to steps 1610-1620 mentioned above. At step1830, a third tracker attached to the intervention tool measures themagnetic field emitted by the first tracker. At step 1840, the relativeposition of the first, second, and third trackers is determined based onthe magnetic field measured by the second and third trackers. At step1850, the respiratory signal is generated based on the relative positionof the first and second trackers. At step 1860, the virtualrepresentation of the intervention tool is generated based on therelative position of the first and third trackers.

FIG. 19 is a flowchart of an exemplary method of indicating when toadvance an intervention tool during an intervention procedure on thesubject (e.g., patient). At step 1910, a patient's respiration ismonitored using an electromagnetic respiration monitor, such as thosementioned above. Next, while monitoring the patient's respiration, thepatient is scanned using a scanner at step 1920 and an image data set isgenerated from the scan at step 1930. At step 1940, the image data setis associated with the respiratory state of the patient at the time ofthe scan. At step 1950, while continuing to monitor the patient'srespiration using the electromagnetic respiration monitor, anintervention tool advancement indicator can indicate when to advance anintervention tool during a subsequent respiratory state of the patientthat matches the respiratory state of the image data set. In thismanner, the advancement indicator can indicate when to advance theintervention tool when the patient's target area is in the same positionas when the scan was taken.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described insome detail, it is not the intention of the applicant to restrict or inany way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention may take form in various compositions,components and arrangements, combinations and sub-combinations of theelements of the disclosed embodiments. Therefore, the invention in itsbroader aspects is not limited to the specific details, representativeapparatus and methods, and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the spirit or scope of the applicant's general inventive concept.

1. An electromagnetic tracking system, comprising: a first trackerattached to a subject, wherein the first tracker comprises an emitter toemit a magnetic field; a second tracker attached to the subject, whereinthe second tracker comprises a first receiver to measure the magneticfield; and logic to determine a position of the second tracker relativeto the first tracker based on the magnetic field measured by the firstreceiver and to generate a respiratory signal based on the position ofthe second tracker relative to the first tracker; wherein the positionof the second tracker relative to the first tracker changes during aplurality of respiratory states of the subject.
 2. The system of claim1, wherein the emitter comprises at least two emitting coils.
 3. Thesystem of claim 1, wherein the first receiver comprises at least tworeceiving coils.
 4. The system of claim 1, wherein the first receivercomprises at least three receiving coils.
 5. The system of claim 1,further comprising: a third tracker attached to the subject, wherein thethird tracker comprises a second receiver to measure the magnetic field;and logic to determine a position of the third tracker relative to thefirst tracker based on the magnetic field measured by the secondreceiver and to generate the respiratory signal based on the position ofthe third tracker relative to the first tracker; wherein the position ofthe third tracker relative to the first tracker changes during theplurality of respiratory states of the subject.
 6. The system of claim5, further comprising: a fourth tracker, wherein the fourth trackercomprises a third receiver to measure the magnetic field; and logic todetermine a position of the fourth tracker relative to the first trackerbased on the magnetic field measured by the third receiver and togenerate the respiratory signal based on the position of the fourthtracker relative to the first tracker; wherein the position of thefourth tracker relative to the first tracker changes during theplurality of respiratory states of the subject.
 7. The system of claim1, further comprising: a fiducial marker, wherein the fiducial marker isviewable in an imaging data set from an imaging device to scan thesubject, wherein the imaging data set is associated with a firstrespiratory state of the subject, and wherein the first respiratorystate of the subject is one of the plurality of respiratory states ofthe subject.
 8. The system of claim 7, further comprising: a thirdtracker associated with an intervention tool, wherein the interventiontool is associated with an intervention procedure performed on thesubject, and wherein the third tracker comprises a second receiver tomeasure the magnetic field; and logic to determine a position of thethird tracker relative to the fiducial marker based on the magneticfield measured by the second receiver.
 9. The system of claim 7, furthercomprising: a universal device, wherein the universal device comprisesthe fiducial marker and at least one of the first tracker and the secondtracker.
 10. An electromagnetic tracking system for indicatingintervention tool advancement timing during an intervention procedure,comprising: an electromagnetic tracking system for monitoringrespiration of a subject, wherein the electromagnetic respirationmonitor produces a respiratory signal indicative of a plurality ofrespiratory states of the subject; the electromagnetic respirationmonitor comprising: a first tracker attached to a subject, wherein thefirst tracker comprises an emitter to emit a magnetic field; a secondtracker attached to the subject, wherein the second tracker comprises areceiver to measure the magnetic field; and logic to determine aposition of the second tracker relative to the first tracker based onthe magnetic field measured by the receiver and to generate therespiratory signal based on the position of the second tracker relativeto the first tracker; wherein the position of the second trackerrelative to the first tracker changes during the plurality ofrespiratory states of the subject; an imaging device for scanning thesubject and generating an imaging data set, wherein the imaging data setis associated with a first respiratory state of the subject; and anadvancement indicator for indicating when to advance an interventiontool based on the respiratory signal, such that advancement of theintervention tool occurs during the first respiratory state of thesubject.
 11. The system of claim 10, further comprising: a fiducialmarker, wherein the fiducial marker is viewable in the imaging data set,and wherein the first respiratory state of the subject is one of theplurality of respiratory states of the subject.
 12. The system of claim11, further comprising: a third tracker associated with the interventiontool, wherein the third tracker comprises a second receiver to measurethe magnetic field; and logic to determine a position of the thirdtracker relative to the fiducial marker based on the magnetic fieldmeasured by the second receiver.
 13. The system of claim 11, furthercomprising: a universal device, wherein the universal device comprisesthe fiducial marker and at least one of the first tracker and the secondtracker.
 14. A electromagnetic tracking method, comprising: emitting amagnetic field from a first tracker, wherein the first tracker isattached to a subject and comprises an emitter to emit the magneticfield; measuring the magnetic field with a second tracker, wherein thesecond tracker is attached to the subject and comprises a first receiverto measure the magnetic field; determining a position of the secondtracker relative to the first tracker based on the magnetic fieldmeasured by the first receiver; and generating a respiratory signalbased on the position of the second tracker relative to the firsttracker; wherein the position of the second tracker relative to thefirst tracker changes during a plurality of respiratory states of thesubject.
 15. The method of claim 14, further comprising: measuring themagnetic field with a third tracker, wherein the third tracker isattached to the subject and comprises a second receiver to measure themagnetic field; and determining a position of the third tracker relativeto the first tracker based on the magnetic field measured by the secondreceiver; and generating the respiratory signal based on the position ofthe third tracker relative to the first tracker; wherein the position ofthe third tracker relative to the first tracker changes during aplurality of respiratory states of the subject.
 16. The method of claim14, further comprising: generating an imaging data set from a scan ofthe subject with an imaging device, wherein the imaging data set isassociated with a first respiratory state of the subject, and whereinthe first respiratory state of the subject is one of the plurality ofrespiratory states of the subject.
 17. The method of claim 16, furthercomprising: providing a fiducial marker, wherein the fiducial marker isviewable in the imaging data set.
 18. The method of claim 17, furthercomprising: measuring the magnetic field with a third tracker, whereinthe third tracker is associated with an intervention tool, wherein theintervention tool is associated with an intervention procedure performedon the subject, and wherein the third tracker comprises a secondreceiver to measure the magnetic field; and determining a position ofthe third tracker relative to the fiducial marker based on the magneticfield measured by the second receiver.
 19. The method of claim 18,further comprising: generating a virtual representation of theintervention tool with an image of the subject, wherein the image isbased on the imaging data set.
 20. The method of claim 17, furthercomprising: providing a universal marker, wherein the universal markercomprises the fiducial marker and at least one of the first tracker andthe second tracker.